1. Field of the Invention
The present invention relates to a hydraulic shock absorber to be used as a suspension system for a vehicle.
2. Description of the Prior Art
A strut type suspension system for a vehicle is constructed such that a hydraulic shock absorber has a piston rod thereof supported on a chassis and a cylinder thereof supported on a wheel through a knuckle so that hydraulic attenuation may be established by the confined oil in response to the sliding movements of a piston fitted in the cylinder, thereby damping and absorbing the shocks coming from a road.
In the hydraulic shock absorber of this kind, friction noises are generated between a piston and cylinder, and between a piston rod and a rod guide during the axial sliding movements of the piston and its rod. In addition, there are generated flapping noises caused by the opening and closing operations of a check valve flapper which is carried on the piston, and concussion noises caused by the fluctuations in the oil pressure. These noises are transmitted to the chassis through the piston rod thereby causing the noises and vibrations. Especially in an otherwise substantially noise-free vehicle in which the prevention and restraint of the noises produced by other causes is of superior quality, the aforementioned noises become clear and prominent to an undesirable level. Moreover, even if the spring of the suspension system is made softer, the aforementioned frictions at the piston, bearing and other parts are directly transmitted through the piston rod to a spring stopper. This constitutes an obstacle to improvement of driving comfortability.
The present invention has been conceived with a view toward effectively solving the aforementioned problem with noises in the vehicular hydraulic shock absorber.